The invention relates to an optical imaging system having an electronically variable focal length, comprising a system of lenses and a liquid crystal layer. The invention also relates to an optical image sensor provided with such an imaging system.
A system of this type is known from German Patent Application No. 28 55 841 laid open to public inspection which corresponds to U.S. Pat. No. 4,190,330. In this Application an optical imaging system is described which consists of a lens-shaped space left in a transparent substrate and coated on the inside with transparent electrodes and orientation layers and which is filled with liquid crystal in the nematic phase. This crystal is birefringent. The refractive index for the extraordinary ray can be varied by applying an electric field. This results in a lens whose power is variable for light in one state of polarization. The ordinary ray for which the refractive index does not vary is suppressed by a polarization filter or is deflected by a second lens of this type whose orientation layers are perpendicular to those of the first lens.
A drawback of the system described in the said German Patent Application No. 28 55 841 is that the range of variation of the focal length is limited by the limited range within which the refractive index of the liquid crystal material can be varied under the influence of the electric field.